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Subject: RE: [PATCH v2 00/11] iommufd: Add nesting infrastructure
Thread-Topic: [PATCH v2 00/11] iommufd: Add nesting infrastructure
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Date:   Wed, 28 Jun 2023 02:47:02 +0000
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> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, June 28, 2023 12:01 AM
>=20
> On Tue, Jun 27, 2023 at 06:02:13AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > Sent: Tuesday, June 27, 2023 1:29 AM
> > >
> > > > I'm not sure whether the MSI region needs a special MSI type or
> > > > just a general RESV_DIRECT type for 1:1 mapping, though.
> > >
> > > I don't quite get this part. Isn't MSI having IOMMU_RESV_MSI
> > > and IOMMU_RESV_SW_MSI? Or does it juset mean we should report
> > > the iommu_resv_type along with reserved regions in new ioctl?
> > >
> >
> > Currently those are iommu internal types. When defining the new
> > ioctl we need think about what are necessary presenting to the user.
> >
> > Probably just a list of reserved regions plus a flag to mark which
> > one is SW_MSI? Except SW_MSI all other reserved region types
> > just need the user to reserve them w/o knowing more detail.
>=20
> I think I prefer the idea we just import the reserved regions from a
> devid and do not expose any of this detail to userspace.
>=20
> Kernel can make only the SW_MSI a mandatory cut out when the S2 is
> attached.
>=20

I'm confused.

The VMM needs to know reserved regions per dev_id and report them
to the guest.

And we have aligned on that reserved regions (except SW_MSI) should
not be automatically added to S2 in nesting case. Then the VMM cannot
rely on IOAS_IOVA_RANGES to identify the reserved regions.

So there needs a new interface for the user to discover reserved regions
per dev_id, within which the SW_MSI region should be marked out so
identity mapping can be installed properly for it in S1.

Did I misunderstand your point in previous discussion?